Conventionally, an image forming apparatus including a main casing, a drum cartridge having a photosensitive drum, and a developing cartridge having a developing roller is known.
It is disclosed that the drum cartridge and the developing cartridge are detachably mounted on the main casing. It is disclosed that the developing cartridge and the drum cartridge can be divided.
The drum cartridge includes a rotatable gear. The gear includes a protrusion. The protrusion moves by rotation of the gear and contacts a movable body of the main casing. The movable body moves by contact with the protrusion. A detecting sensor included in the main casing detects movement of the movable body. Thereby, the image forming apparatus determines whether the drum cartridge is new or used.